Virtually all persons engaged in firearm shooting, whether hunting or target shooting, are well aware of at least some of the basic factors affecting the accuracy of a shot. The primary factors affecting shooting accuracy are the range or distance to the target and resulting arcuate trajectory (drop) of the bullet, and windage or lateral drift due to wind. The need to correct for these two factors is well known.
However, there are several other factors which result in lesser errors in shooting. Nevertheless, it is critical that these other factors be taken into consideration and compensated for, to produce an extremely accurate shot. These factors are especially critical at long ranges, i.e. approaching or over one thousand yards.
One factor which appears fairly often in the field is slope. The difference in elevation between the firearm and the target can result in significant error, depending upon the elevation difference and the range of the shot. While various corrections have been developed for most of these factors, most such corrections have been provided in the form of mathematical equations, the solution of which is left to the user's discretion as to how to accomplish the mathematics.
Other factors are atmospheric variables, specifically altitude and barometric pressure, temperature, and humidity. These variables have traditionally been utilized to alter the ballistic coefficient (BC) of a projectile for specific atmospheric conditions prior to calculating the trajectory. BC is a scaling factor against a well-known, standard projectile. These atmospheric variables all affect the aerodynamic drag on the projectile, thus altering the trajectory.
Certain telescopic firearm sight reticles have been developed in the past, with various markings to assist the shooter in determining the apparent range of a target. A nearly universal system has been developed by the military for artillery purposes, known as the “mil-radian,” or “mil,” for short. This system has been adopted by most of the military for tactical (sniper) use, and subsequently adopted by most of the sport shooting world. The mil is an angle having a tangent of 0.001. This provides a means of measuring the distance to a target in terms of apparent target height or span (or height or span of a known object in the vicinity of the target). For example, a target distance of one thousand yards would result in one mil subtending a height of one yard, or thirty six inches, at the target. This is about 0.058 degree, or about 3.5 minutes of angle. It should be noted that although the term “mil-radian” implies a relationship to the radian, the mil is not exactly equal to an angle of one thousandth of a radian, which would be about 0.057 degree or about 3.42 minutes of angle. The “mil-dot” system, based upon the mil, is in wide use in scope reticle marking, but does not provide any means per se of determining the distance to a target without having at least a general idea of the target size, and performing a mathematical calculation involving these factors.
Another angular measurement system used in shooting is known as the “minute of angle,” or MOA. This system measures the height or distance subtended by an angle of one minute, or one sixtieth of a degree. At a range of one hundred yards this subtended span is slightly less than 1.05 inches, or about 10.47 inches at one thousand yards range. It will be seen that the distance subtended by the MOA is substantially less than that subtended by the mil at any given distance, i.e. thirty six inches for one mil at one thousand yards but only 10.47 inches for one MOA at that range.
Both of the above described systems are in use for scope reticle marking, and either may be incorporated with the present nomograph system. Both are angular measurements, however, they require that some dimension of the target (or object near the target) be known in order to determine the distance to the target by means of the mil or MOA angular systems.
In addition to the above general knowledge of the field of the present invention, the present inventor is also aware of certain foreign references:
Japanese Patent Publication No. 55-36,823 published on Mar. 14, 1980 to Raito Koki Seisakusho KK describes (according to the drawings and English abstract) a variable power rifle scope having a variable distance between two horizontally disposed reticle lines, depending upon the optical power selected. The distance may be adjusted to subtend a known span or dimension at the target, with the distance being displayed numerically on a circumferential external adjustment ring. A prism transmits the distance setting displayed on the external ring to the eyepiece of the scope, for viewing by the marksman.
German Patent Publication No. 3,401,855 published on Jul. 25, 1985 to Carl Walther GMBH describes (according to the drawings and English abstract) a toroidal ring attached to the eyepiece end of a firearm scope, with the ring being half filled with a highly visible liquid. Aligning the liquid level with the ends of the horizontal stadia of the reticle, assures that the firearm scope is leveled axially.
German Patent Publication No. 3,834,924 published on Apr. 19, 1990 to Siegfried Trost describes (according to the drawings and English abstract) a scope leveling device similar to that of the '855 German Patent Publication noted immediately above, but containing a weight in a semicircular tubular segment, rather than a liquid in a toroidal ring.
Given certain existing drawbacks, what is needed, therefore, are new systems and devices for resolving factors affecting the trajectory of a bullet fired from a firearm. It is to the provision of such nomographs and charts that provide solutions for factors involved in the ballistic flight of a bullet or projectile that the various embodiments of the present invention are directed.